Field of the Invention
The invention relates to a method and a device for determining the ambient pressure for an internal combustion engine and to an air mass meter for the device.
The ambient air pressure is evaluated by a number of control systems involved in controlling operation of an internal combustion engine. In view of this fact, there is often provided a corresponding ambient pressure sensor in a control unit.
The ambient pressure can be used, for example, to determine the degree of loading of an air filter that is connected upstream of the intake tract of the internal combustion engine. If the absolute pressure in the intake pipe downstream of the air filter is measured in front of a throttle valve, it is possible, if the pressure difference between this absolute pressure and the ambient pressure exceeds a threshold which is dependent on operating parameters, to conclude that the pressure drop at the air filter is excessive.
The ambient pressure may also be taken into account when determining the injection times.
According to the prior art, an ambient pressure pick-up is indispensable for measuring the ambient pressure. For example, German published patent application DE 44 26 272 A1 provides a pressure gauge in the intake tract and a separate ambient pressure pick-up. Both feed their measured values to a control unit which in addition is connected to a temperature sensor disposed in the intake tract.
German published patent application DE 39 14 784 A1 dispenses with the option of constant measurement and uses an absolute pressure pick-up downstream of a throttle valve in the intake tract, the value from which pick-up is read only above a minimum opening angle of the throttle valve.
The object of the invention is to provide a method and device for determining the ambient pressure at an internal combustion engine and an air mass meter therefor which overcomes the above-noted deficiencies and disadvantages of the prior art devices and methods of this kind.
With the above and other objects in view there is provided, in accordance with the invention, a method of determining an ambient pressure for an internal combustion engine, with an air mass meter in. the intake tract. The method comprises the following steps: measuring a starting or initial value for an ambient pressure, an air mass flow rate, an air temperature, and an absolute pressure in an intake tract of an internal combustion engine upstream of a throttle member in an intake air flow direction; and determining an ambient pressure prevailing outside the intake tract from the starting value for the ambient pressure, the air mass flow rate, the air temperature, and the absolute pressure.
The method according to the invention is based on the recognition that the pressure drop between an air filter and a throttle member in the intake tract of the internal combustion engine is a function of the pressure loss coefficient in the intake tract and of the air mass flow rate, the air temperature and the ambient pressure. Adding the pressure drop to the absolute pressure in the intake tract gives the ambient pressure. Therefore, there are two recommended variants for determining the ambient pressure.
Firstly, the equation which can be derived from this addition can be suitably rearranged so that the ambient pressure results as a function of the air mass flow rate, the air temperature and the pressure loss coefficient in the intake tract and of the absolute pressure in the intake tract. Secondly, it is possible to use a recursive method, in which, working on the basis of a starting value for the ambient pressure, firstly the pressure drop is calculated and from this, together with the absolute pressure in the intake tract, a new value is obtained for the ambient pressure. It is thus possible to determine the ambient pressure by recursion. The starting value may, for example, be produced by measuring the absolute pressure in the intake tract when the internal combustion engine is stationary or idling, since in these situations the absolute pressure in the intake tract substantially equates to the ambient pressure.
In accordance with an added feature of the invention, a pressure loss coefficient is taken into account, and the pressure loss coefficient is chosen in dependence on a cross-sectional area of the intake tract in a region of the air mass measurement and/or a pressure loss factor representing a flow condition in the intake tract.
In accordance with an additional feature of the invention, a pressure drop between an air filter and the throttle member in the intake tract is determined in dependence on the air mass flow rate, the air temperature, the pressure loss coefficient, and the starting value for the ambient pressure; and a new value for the ambient pressure is calculated by adding the absolute pressure in the intake tract and the pressure drop. The absolute pressure is preferably determined with the internal combustion engine at standstill or in idling.
In accordance with another feature of the invention, the pressure loss coefficient is calculated from the pressure drop, using the ambient pressure, the air mass flow rate and the air temperature, and, if a threshold is exceeded, a signal is emitted indicating a necessity to exchange the air filter upstream of the intake tract in the intake air flow direction.
In accordance with a further feature of the invention, the pressure drop is defined as a difference between ambient pressure and absolute pressure in the intake tract. In the alternative, the pressure drop is directly present.
In accordance with again an added feature of the invention, the pressure loss coefficient is calculated with the equation             C      b        =          Δ      ⁢              xe2x80x83            ⁢              p        ·                              p            u                                              Q              2                        ⁢            T                                ,
where Cb is the pressure loss coefficient, pu is the ambient pressure, xcex94p is a pressure drop, Q is the air mass flow, and T is the air temperature.
In accordance with again an additional feature of the invention, the starting value is the absolute pressure in the intake tract, which equates to the ambient pressure;
the absolute pressure is continuously recorded during a subsequent start-up; and
the pressure loss coefficient is calculated with the equation             C      b        =                  (                              p            u                    -                      p            s                          )            ·                        p          u                                      Q            2                    ⁢          T                      ,
xe2x80x83where Cb is the pressure loss coefficient, pu is the ambient pressure, ps is the absolute pressure, Q is the air mass flow rate, and T is the air temperature in the intake tract;
the pressure loss coefficient Cb is stored in a characteristic diagram as a function at least of the air mass flow rate Q, which represents an operating parameter of the internal combustion engine; and
during further determination of the ambient pressure pu, values of the characteristic diagram as a function of operating parameters are taken into account for the pressure loss coefficient Cb.
With the above and other objects in view there is also provided, in accordance with the invention, a device for determining an ambient pressure for an internal combustion engine with an intake tract, comprising:
an air mass meter in an intake tract of an internal combustion engine;
an absolute pressure pick-up connected to the air mass meter;
a temperature sensor;
a control unit connected to the air mass meter, to the absolute pressure pick-up, and to the temperature sensor, the control unit being configured to determine an ambient pressure pu in accordance with the method according to claim 1, without an ambient pressure pick-up.
There is also provided, in accordance with the invention, an air mass meter for the above-outlined device. The novel air mass meter comprises:
a housing attached to the intake tract of the internal combustion engine and communicating therewith through a passage connecting the housing to the intake tract for pressure compensation purposes;
an air mass sensor mounted at the housing and projecting into the intake tract; and
an absolute pressure sensor.
In accordance with yet another feature of the invention, the housing has an electrics housing which houses the absolute pressure sensor and including a connector, providing electrical contact with the air mass sensor and the absolute pressure sensor.
In accordance with yet an added feature of the invention, the housing includes a section of pipe configured to fit into the intake tract, enclosing the air mass sensor, and supporting the electrics housing, and wherein the passage connects the electrics housing to the section of pipe.
In accordance with a concomitant feature of the invention, a circuit board is supported on a base of the electrics housing, the circuit board supporting the absolute pressure sensor and the air mass sensor being connected to the circuit board, and a layer, applied in liquid form and hardened, disposed on the circuit board for pressure transfer and for protecting the absolute pressure sensor, the circuit board, the absolute pressure sensor, and the connection wires, and wherein a connection piece is formed at the passage for preventing a material of the layer from being able to pass into the passage before the material cures.
In other words, the device according to the invention provides an air mass meter between an air filter and a throttle member in the intake tract, in which there is an absolute pressure pick-up and an air temperature sensor in the intake tract, which are connected to a control unit which, when carrying out the method according to the invention, no longer has to have recourse to an ambient pressure signal in order to calculate the ambient pressure.
The air mass meter according to the invention for this device has the air mass sensor and an absolute pressure sensor in a housing, so that the essential components of the device are produced in a compact, simple component which is inexpensive to produce. Furthermore, this air mass meter has the additional advantage that cabling and plug connections, which represent relatively expensive components, are simplified.
The pressure loss coefficient in the intake tract is decisively characterized by the pressure drop at the air filter. The loading of the air filter is substantially responsible for the pressure drop. However, this loading only varies slowly with respect to ambient pressure. Furthermore, the level of loading of the air filter does not have any effect on the air pressure in the intake tract if there is no or virtually no air mass flow being sucked in. This is the case when the internal combustion engine is at a standstill or idling.
It is thus possible for the pressure loss coefficient which is used in the calculation of the pressure value in accordance with the first variant to be calibrated or determined by means of an absolute pressure measurement in the intake tract when the internal combustion engine is at a standstill or idling. Once this value has been determined, it can then be used to carry out the rest of the method.
If the pressure loss coefficient exceeds a predetermined threshold, it is possible to draw the conclusion that the air filter is too strongly loaded, i.e. is causing an excessive pressure drop.
The invention therefore has the advantage that it is possible to dispense with a separate ambient pressure pick-up in order to determine the ambient pressure. Furthermore, it is possible to determine the level of loading of the air filter and thus to establish when it needs to be exchanged.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a method and device for determining the ambient pressure in an internal combustion engine, and air mass meter therefor, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.